Method and apparatus for forming articles from plastic sheet material

ABSTRACT

A vacuum-forming apparatus and method for making a pair of adjacent compartment liners from a single sheet of thermoplastic material. In the apparatus aspect, a pair of adjacent molds, each affording the desired shape of the inside surface of the corresponding liner to be formed, are mounted along their base portions on a frame structure hinged in the region of adjacency of the mold base portions, to provide for pivotation of the respective base portions so that confronting surfaces of the molds are movable angularly toward and away from one another. Table structure supports the pivotable frame structure and is mounted for tilting about an axis generally parallel to the axis of pivotation of the molds. In the method aspect, a sheet of thermoplastic material is disposed to extend over the molds and is heated to a pliable, softened state while the molds are held in pivoted positions, in which the confronting surfaces are substantially spaced from one another, and while the table structure is held in upwardly tilted position. The pliable sheet of thermoplastic material is then caused to billow away from the pivoted and tilted molds, whereupon mold assist-plugs and the molds are then moved, relatively, toward one another, to urge the sheet to generally close conformity with the molds. While the sheet of thermoplastic material is still pliable, the frame structure is pivoted to cause confronting adjacent wall portions of the mold to move toward one another and assume a closely spaced relation, while the table structure is moved from its tilted position to a substantially horizontal position. Air entrapped between the pliable sheet and the walls of the molds is then evacuated through a number of small ports or vents in the walls, thereby forming the desired liners over the molds. The liners are then cooled and stripped as a unit from the molds.

United States Patent 1 Smith [451 Apr. 22, 1975 METHOD AND APPARATUS FORFORMING ARTICLES FROM PLASTIC SHEET MATERIAL Related US. ApplicationData Primary Examiner-R. Spencer Annear Attorney, Agent, or FirmRobertD. Sanborn [57] ABSTRACT A vacuum-forming apparatus and method formaking a pair of adjacent compartment liners from a single sheet ofthermoplastic material. In the apparatus aspect. a pair of adjacentmolds, each affording the desired shape of the inside surface of thecorresponding liner to be formed. are mounted along their base portionson a frame structure hinged in the region of adjacency of the mold baseportions, to provide for pivotation of the respective base portions sothat confronting surfaces of the molds are movable angularly toward andaway from one another. Table structure supports the pivotable framestructure and is mounted for tilting about an axis generally parallel tothe axis of pivotation of the molds. ln the method aspect, a sheet ofthermoplastic material is disposed to extend over the molds and isheated to a pliable, softened state while the molds are held in pivotedpositions, in which the confronting surfaces are substantially spacedfrom one another, and while the table structure is held in upwardlytilted position. The pliable sheet of thermoplastic material is thencaused to billow away from the pivoted, and tilted molds, whereupon moldassist-plugs and the molds are then moved, relatively, toward oneanother, to urge the sheet to generally close conformity with the molds.While the sheet of thermoplastic material is still pliable, the framestructure is pivoted to cause confronting adjacent wall portions of themold to move toward one another and assume a closely spaced relation.while the table structure is moved from its tilted position to asubstantially horizontal position. Air entrapped between the pliablesheet and the walls of the molds is then evacuated through a number ofsmall ports or vents in the walls, thereby forming the desired linersover the molds. The liners are then cooled and stripped as a unit fromthe molds.

6 Claims, 7 Drawing Figures METHOD AND APPARATUS FOR FORMING ARTICLESFROM PLASTIC SHEET MATERIAL CROSS REFERENCE TO RELATED DISCLOSURE Thisis a division of Application Ser. No. 384,636. Filed Aug. 1. 1973.

This invention is directed to improvements in the method and apparatusdisclosed and claimed in the copending application of Norman F.Houghton. Ser. No. 235.968 filed Mar. 20. 1972. now Pat. No. 3.781.394.and assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION This invention relates to the formation ofarticles from sheets of thermoplastic material. and is more particularlyconcerned with an improved method and apparatus for forming deep-drawnshapes. for example food storage compartment liners for refrigeratorcabinets.

In producing articles of the aforementioned type. it is known to bringan assist-plug into contact with a heat-softened. pliable sheet ofthermoplastic material to urge portions thereof onto adjacent formingmolds. after which the material is subjected to a vacuum. while in itspliable state to achieve a desired shape. In the fabrication of linersfor dual-compartment refrigerators, it has been desired to mold theliners from a single sheet. but it has been found difficult to achieveuniform thickness of the sheet in the region of the adjacent walls ofthe liners. due to the close spacing therebetween. and further tocontrol the thickness of the sheet in regions of certain outer walls ofthe liners.

It is a general objective of this invention to provide an improvedforming apparatus and method which overcomes the above-mentioneddifficulties. and is useful in fabrication of plural-compartment cabinetliners. for either vertical or horizontal disposition.

SUMMARY OF THE INVENTION In achievement of the foregoing as well asother objectives and advantages. the invention contemplates improvementsboth in a method of. and apparatus for. forming an article from a sheetof thermoplastic material. which article in preferred practice of theinvention comprises a pair of adjacent walled structures. havingunidirectionally presented openings. In accordance with theaforementioned preferred practice. the invention features provision of apair of unidirectionally presented molds shaped in correspondence to thestructures to be formed and so associated as to be movable between oneposition in which confronting walls thereof are closely spaced inaccordance with the spacing of the structures to be formed. and anotherposition in which said confronting walls are spaced apart asubstantially greater distance than in said one position. whereinimprovement resides in provision for: tilting said molds about an axisextending generally transverely of the direction of relative movement ofsaid molds; movement of said molds to the mentioned other position inwhich the confronting walls of said molds are substantially spaced;extension of a unitary, softened sheet of thermoplastic material oversaid tilted and pivoted molds; billowing of said softened sheet awayfrom said molds; relative translation of said spaced-apart. tilted moldsand said billowed sheet toward one another sufficient to engage thetilted and spaced-apart molds therewith while said sheet is engaged byan assist-plug to stretch the softened sheet over said molds; movementof said molds to horizontal non-tilted position and to said one positionin which they are closely spaced; and utilization of differential fluidpressure to cause said softened sheet to conform to the surfaces of saidmolds in said one. closely spaced. non-tilted position.

Advantageously, the combined tilting and relative pivotation of the moldmembers ensures presence of ample material in regions of relatively deepdraw. whereby there is achieved a molded article of substantiallyuniform wall thickness.

The manner in which the foregoing as well as other objectives andadvantages of the invention may best be achieved will be more fullyunderstood from a consideration of the following description. taken inlight of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational showing ofrefrigerator cabinet structure of a type embodying a pair of compartmentliners made in accordance with the invention. and with the doors removedfor convenience of illustration:

FIG. 2 is a sectional showing of the cabinet structure taken generallyalong the line indicated by arrowe 2-2 applied to FIG. 1; 9

FIG. 3 is a sectional-elevational view. with some parts fragmented forconvenience of illustration. of mold apparatus for fabricating thecompartment liners of the cabinet seen in FIGS. 1 and 2. and furtherillustrating operational features of the apparatus contemplated by theinvention; and.

FIGS. 4 to 7 are further showings of a portion of the apparatus seen inFIG. 3. and illustrating further opera-- tional features thereof.

DESCRIPTION OF THE PREFERRED PRACTICE AND APPARATUS With reference toFIGS. 1 and 2. a refrigerator cabinet I0 includes a pair of compartmentshaving unidirectionally presented openings. and defined by a pair oflinear sections 11 and 12. The liner sections are made of athermoplastic material. such as. for example. ABS resin. and are moldedas an integral structure from a single flat sheet of such material. inaccordance with the invention to be described in detail below. Thermalinsulation designated generally by the numeral 13. and which may forexample be of the foamed type. fills the spaces between the confrontingwalls of liner sections 11 and I2, and between the outer walls of thesame sections and the walls of outer shell 14 of cabinet 10. It will beunderstood. of course. that other well-known. suitable types of thermalinsulation may be used.

The refrigerating unit is conventional. comprising a compressor 15,condenser 16. and an evaporator l7 connected in the usual series flowcircuit by suitable conduit means (not shown). Evaporator l7conveniently located in a recessed portion 21 of upper liner section II,and a partition 22 includes a horizontal section that extends over therecess and the evaporator.

The hereinabove-identified copending application is directed to a novelmethod and apparatus for molding liner structure including an undercutsection such as recessed portion 21. Further to the exemplaryrefrigerator construction. partition 22 is provided with front airpassages 23. and a vertical section 22a of the partition is spaced fromthe top and rear walls of liner section 1] as shown. Air moved by ablower 24 disposed in the rear portion of recess 21 is caused to flowinto the freezer storage compartment defined by liner section 11,through the space between the liner and partition 22a, thence returns tothe region of evaporator I7 through front passages 23. The lower foodstorage compartment, defined by liner section 12. is cooled by aircaused to move from the compartment through pas sages 25, overevaporator 17. thence back into the compartment through passages 26.

It will be appreciated that the invention to which the copendingapplication is directed overcomes problems arising from: thecharacteristically close spacing between the above-described upper andlower lines sections 11 and 12. which heretofore had made it difficultto vacuum-form the confronting top and bottom walls of the liners. dueparticularly to the relatively small amount of thermoplastic materialavailable in the blank sheets for the relatively deep draw required inthis region; and the fact that the recessed portion 21 of the upperliner section 11 comprises an undercut section. making it difficult toprovide mold structure from which the molded liners may be easilystripped.

It will be further appreciated that the present invention recognizes,and provides a solution to. problems associated with a scarcity ofmaterial for molding the top wall of liner section 11. Material isscarce in this re gion due to the relatively small projected area of theplastic sheet undergoing deep draw to form the freezer compartment linersection 11. as compared with the relatively large projected areaundergoing the same depth of draw to form the food compartment linersection 12.

Turning now to apparatus for forming liners 11 and I2 in accordance withthe invention. and first with reference to FIG. 3, an open top.generally box-shaped chamber is ported. at 31, to suitable pressureproducing mechanism of conventional design (not shown). A clamping ring33 closely surrounds the upper rim of chamber 30, and is constructed andarranged to clamp in place a sheet of thermoplastic material M (brokenline showing) that extends over the upper rim of chamber 30. A radiantheater 34 is arranged to overlie the sheet to heat the same. and ismounted for lateral movement (sec horizontal arrows) between theillustrated extended position and a retracted position in which it isremoved from above the sheet. An assistplug 35 of generally rectangularshape is disposed above heater 34 and has a slightly rounded edgeportion 36 as viewed in section. Relative movement between the plug andthe mold is provided for by mounting both assist-plug 35 and the molds37 and 38 for vertical movements. into and out of telescopingrelationship. as will be described in detail. No specific apparatus formoving the assist-plug and molds has been shown, since this apparatuscan be entirely conventional in nature.

Each of the adjacently positioned. generally unidirectionally presentedmolds 37 and 38 is shaped to yield the general box-shape of the insidesurfaces of the respective liner sections 11 and 12 to be molded. Molds37 and 38 are mounted along their base portions on articulated framestructure 40 hinged at 41 in the region of adjacency of the mold baseportions. Use of two molds, and if hinged mold-supporting framestructure. is in accordance with the hereinabove-indentified copendingapplication. In further accordance with the copending application. theleft-hand. smaller mold 37 includes an auxiliary section 42 nested inmold 37 for selective extensible movement on runners 44 through opening43 into the space between the molds 37 and 38. whereby in extendedposition it affords. together with mold 37, the desired shape of thesmaller liner section 11 to be formed. Movements of auxiliary section 42are afforded by a suitable pneumatic linkage of known type. anddesignated generally by the numeral 50. Frame structure 40 is suitablyported at 51 and 52, and molds 37. 38 and 42 are provided with largenumbers of vents or ducts, of a type appearing on enlarged scale at 53.

In especial accordance with the present invention. frame structure 40further is supported for both sliding and pivotal movements on a tilttable structure 56 carried by rectangular. box-shaped support frame 54.Tilt table structure 56 is tiltable on hinge 57 provided on frame 54,about an axis parallel to. and spaced from. the axis of pivotation ofmolds 37 and 38 on hinge 41. Support frame 54, along with the tilt tablestructure 56 and molds thereon. are elevatable from the position shownin FIG. 3 to the upper position shown in FIG. 7. for reasons to be morefully explained. in which upper position the level of the framestructure 40. and mold base portions thereon. are substantially at thelevel of the upper edge of chamber 30. For convenience of illustrationmolds 37 and 38 are shown in full lines in FIG. 3 in their upwardlypivoted and tilted positions. The lower. pivoted position of mold 37 isshown partly in broken lines. in order to illustrate advantages affordedby the invention arising from the lateral displacement G (FIG. 3)afforded by tilting of table structure 56, as will be explained inconnection with operation of the apparatus.

The upwardly pivoted position of frame structure 40 is maintained bymechanism including pneumatic linkage means 59 carried by tilt tablestructure 56, and tilting of table structure 56 about its hinge 57 isprovided by a pneumatic linkage means 58 on frame 54. both said linkagemeans being of well-known type. Support frame 54 further includescombination vacuumpressure connections 60 and 61. of known type. forintroducing. selectively. vacuum or pressure to the underside of molds37 and 38, while in their non-pivoted. non-tilted positions.Conveniently. connections 60 and 61 comprise flexible hoses or linesextending in airtight relation through chamber 30 for connection tosuitable pressure and vacuumproducing means of conventional design. Itwill be understood that the other known connection means may be providedto accommodate vertical movements of the molds in chamber 30. Forexample. connections utilizing telescoping fluid-tight couplings may beused. either singly or in combination with flexible lines. The upperends of connections 60 and 61 terminate in sealing rings 62 and 63provided in tilt table structure 56, which rings are positionedsealingly to engage respectively aligned ports SI and 52 in framestructure 40 communicating with the hollow undersides of molds 37 and 38(see FIG. 3).

In the formation of a pair of liners Ill and 12., and again withreference to FIG. 3, a sheet of thermoplastic material. shown in brokenlines at M. is placed between assist-plug 35 and molds 37 and 38. Thesheet material is then heated. causing it to soften and sag to theposition seen in full lines at M. while molds 3'7 and 38 are held intheir non-pivoted. non-tilted positions (not sure to chamber by way ofport 31 provided for that v purpose. While the sheet M is in upwardlybillowed position. table structure 56 is held in upwardly. tiltedposition. and molds are held in pivoted position in which theirconfronting surfaces are more widely spaced. At this stage. a furtherrealization may be had of the gain in material M afforded by thedisplacement G referred to in connection with the description of FIG. 3.It is this gain in material that ensures adequate wall thickness in thecorresponding corner region of the molded article as previouslydescribed.

Now with reference to FIG. 5, assist-plug 35 is moved downwardly toengage billowed sheet M. forming a pair of individual, symmetricallybillowed portions, each opposite a corresponding mold 37 and 38. Supportframe 54 is then elevated to move molds 37 and 38 toward the billowed.heat-softened sheet M. as seen in FIG. 6. to engage the sheet andthereafter to urge it onto both molds 37 and 38, while auxiliary moldsection 42 is held in its retracted position.

This movement is then followed by continued elevation of support frame54, and movement of molds 37 and 38 to non-pivoted. non-tilted.liner-forming position by operation of corresponding linkages 58 and 59,in which position the confronting surfaces of molds 37 and 38 arerelatively closely spaced. as is seen in FIG. 7. and sealing rings 62and 63 sealingly engage aligned ports 51 and 52 (FIG. 3). Upon this andthe ensuing movements for the final stages of the molding operation.there are realized the advantages afforded by the gain of extra materialboth between molds 37 and 38.. and at the upper left edge of mold 37.

With further reference to FIG. 7, assist-plug 35 is retracted to itsupper position. a vacuum is created first in right-hand mold 38 throughconnection 61, and air entrapped between the heated sheet and right-handmold 38 is removed through the large number of vents or ports 53 in thewalls thereof. causing the right-hand sheet portion to conform to themold 38 and form the desired liner section 12, on mold 38 as shown.Immediately. and still with reference to FIG. 7, the auxiliary section42 of mold 37 is projected to its extended position by pneumatic linkage50. While auxiliary section 42 is held in its extended position. airentrapped between the heated sheet and mold 37, and its auxiliarysection 42. is evacuated through connection 60 to form the desired linersection 11 and its undercut region 21 (FIG. 2). Liner sections 11 and 12are then cooled. the extended auxiliary mold section 42 is retractedfrom the undercut region of liner section 11, and the integrally formedliner sections are ready for stripping from the molds. Formation ofcommunicating passages between the upper and lower refrigeratorcompartments, examples of such passages being the air passages 25 and 26seen in FIGS. 1 and 2, is provided, prior to stripping of the liners andaccording to the method disclosed and claimed in copending applicationoflohn A. Scarlett. Ser. No. 311,722 filed Dec. 7, 1972, now Pat. No.3.834.177. and assigned to the assignee of the present invention.

While the invention has been described in connection with the formationof refrigerator compartment liners. it will be understood that theinvention as claimed contemplates the formation of compartmentedstructures. generally. Also, it will be understood thatpressurizedequipment may be used in place of the vacuum apparatus asshown and described for the application of differential fluid pressureto the softened thermoplastic sheet.

I claim:

1. In apparatus for forming a deep-drawn. unitary, plastic articlecomprising a pair of adjacent walled structures having unidirectionallypresented openings. said apparatus being of the type including a pair ofspaced. unidirectionally presented molds having outer surface portionscorresponding to the'shape of the article to be formed. an assist-plugstructure at least a portion of which is insertable into the spacebetween said unidirectionally presented molds. means for supporting aheat-softened. unitary sheet of thermoplastic material between saidmolds and said assist-plug structure. means for effecting relativemovement between said molds and said assist-plug structure to cause themto bear against said sheet. and means for producing a pressuredifferential across opposite surfaces of each of said molds. theimprovements comprising: means for movably mounting said said molds sothat in one position thereof confronting mold wall sections are closelyspaced. and in another position said wall sections are substantiallyspaced; table structure supporting said movable molds and mounted fortilting movements from a substantially horizontal position about an axisextending transversely of the direction of movements of said molds;means for maintaining said molds in said other. substantially spacedposition. and said table structure in its upwardly tilted position. assaid molds and said assist-plug are moved together against said sheet;and means for moving said molds to said one. closely spaced position andsaid table structure to its horizontal, non-tilted position prior tooperation of said means for producing the recited pressure differential.

2. Apparatus according to claim 1, and characterized by the inclusion ofarticulated base means for supporting said molds in such manner that therecited movements thereof are pivotal about an axis generally parallelto the axis about which said table structure is tilted.

3. Apparatus according to claim 2, and further characterized in thatsaid means for maintaining said molds in said other position compriseslinkage means automatically operable upon the recited movement of saidmolds and said assist-plug against said sheet.

4. Apparatus according to claim 1 and characterized by the inclusion ofmeans for supporting said molds in such manner that the recitedmovements thereof are pivotal.

5. In apparatus for forming a deep-drawn. unitary. plastic articlecomprising a pair of walled tank-like structures having unidirectionallypresented openings and adjacent side walls disposed in spaced relation.said walls being joined by. flanging extending generally in the plane ofthe openings of said tank-like structures. said apparatus being of thetype including a pair of similarly spaced. unidirectionally presentedmolds having convex surface portions corresponding to the concave shapeof the tank-like structures to be formed. an assist-plug structure atleast a portion of which is insertable into the space between theadjacent side walls of said unidirectionally presented molds. means forsupporting a heat-softened unitary sheet of thermoplastic materialbetween said molds and said assist-plug structure, means for effectingrelative movement between said molds and said assist-plug structure tocause them to bear against said sheet. and means for producing apressure differential across opposite surface portions of said molds.the improvement comprising: means for movably mounting said molds sothat in one position thereof confronting wall sections corresponding tosaid adjacent walls of said tank-like structures are closely spaced, andin another position said wall section are substantially spaced; tablestructure supporting said movable molds and mounted for tiltingmovements from a substantially horizontal position about an axisextending transversely of the direction of movements of said molds:means for effecting the recited relative movement between said molds andsaid assist-plug structure while said wall sections of said molds are insaid other substantially spaced position and said table structure in itsupwardly tilted position; and means for producing the recited pressuredifferential while the molds are in said one closely spaced position andsaid table structure is in its substantially horizontal position.

6. Apparatus according to claim 5 and characterized in that said meansfor movably mounting said molds comprises articulated based structurehinged along an axis substantially parallel to the axis of tiltingmovements of said table structure. whereby the recited movement of saidmolds in pivotal.

1. In apparatus for forming a deep-drawn, unitary, plastic articlecomprising a pair of adjacent walled strucTures having unidirectionallypresented openings, said apparatus being of the type including a pair ofspaced, unidirectionally presented molds having outer surface portionscorresponding to the shape of the article to be formed, an assist-plugstructure at least a portion of which is insertable into the spacebetween said unidirectionally presented molds, means for supporting aheat-softened, unitary sheet of thermoplastic material between saidmolds and said assist-plug structure, means for effecting relativemovement between said molds and said assist-plug structure to cause themto bear against said sheet, and means for producing a pressuredifferential across opposite surfaces of each of said molds, theimprovements comprising: means for movably mounting said said molds sothat in one position thereof confronting mold wall sections are closelyspaced, and in another position said wall sections are substantiallyspaced; table structure supporting said movable molds and mounted fortilting movements from a substantially horizontal position about an axisextending transversely of the direction of movements of said molds;means for maintaining said molds in said other, substantially spacedposition, and said table structure in its upwardly tilted position, assaid molds and said assist-plug are moved together against said sheet;and means for moving said molds to said one, closely spaced position andsaid table structure to its horizontal, non-tilted position prior tooperation of said means for producing the recited pressuredifferential.
 1. In apparatus for forming a deep-drawn, unitary, plasticarticle comprising a pair of adjacent walled strucTures havingunidirectionally presented openings, said apparatus being of the typeincluding a pair of spaced, unidirectionally presented molds havingouter surface portions corresponding to the shape of the article to beformed, an assist-plug structure at least a portion of which isinsertable into the space between said unidirectionally presented molds,means for supporting a heatsoftened, unitary sheet of thermoplasticmaterial between said molds and said assist-plug structure, means foreffecting relative movement between said molds and said assist-plugstructure to cause them to bear against said sheet, and means forproducing a pressure differential across opposite surfaces of each ofsaid molds, the improvements comprising: means for movably mounting saidsaid molds so that in one position thereof confronting mold wallsections are closely spaced, and in another position said wall sectionsare substantially spaced; table structure supporting said movable moldsand mounted for tilting movements from a substantially horizontalposition about an axis extending transversely of the direction ofmovements of said molds; means for maintaining said molds in said other,substantially spaced position, and said table structure in its upwardlytilted position, as said molds and said assist-plug are moved togetheragainst said sheet; and means for moving said molds to said one, closelyspaced position and said table structure to its horizontal, non-tiltedposition prior to operation of said means for producing the recitedpressure differential.
 2. Apparatus according to claim 1, andcharacterized by the inclusion of articulated base means for supportingsaid molds in such manner that the recited movements thereof are pivotalabout an axis generally parallel to the axis about which said tablestructure is tilted.
 3. Apparatus according to claim 2, and furthercharacterized in that said means for maintaining said molds in saidother position comprises linkage means automatically operable upon therecited movement of said molds and said assist-plug against said sheet.4. Apparatus according to claim 1 and characterized by the inclusion ofmeans for supporting said molds in such manner that the recitedmovements thereof are pivotal.
 5. In apparatus for forming a deep-drawn,unitary, plastic article comprising a pair of walled tank-likestructures having unidirectionally presented openings and adjacent sidewalls disposed in spaced relation, said walls being joined by flangingextending generally in the plane of the openings of said tank-likestructures, said apparatus being of the type including a pair ofsimilarly spaced, unidirectionally presented molds having convex surfaceportions corresponding to the concave shape of the tank-like structuresto be formed, an assist-plug structure at least a portion of which isinsertable into the space between the adjacent side walls of saidunidirectionally presented molds, means for supporting a heat-softenedunitary sheet of thermoplastic material between said molds and saidassist-plug structure, means for effecting relative movement betweensaid molds and said assist-plug structure to cause them to bear againstsaid sheet, and means for producing a pressure differential acrossopposite surface portions of said molds, the improvement comprising:means for movably mounting said molds so that in one position thereofconfronting wall sections corresponding to said adjacent walls of saidtank-like structures are closely spaced, and in another position saidwall section are substantially spaced; table structure supporting saidmovable molds and mounted for tilting movements from a substantiallyhorizontal position about an axis extending transversely of thedirection of movements of said molds; means for effecting the recitedrelative movement between said molds and said assist-plug structurewhile said wall sections of said molds are in said other substantiallyspaced position and said table structure in its upwardly tiltedpositioN; and means for producing the recited pressure differentialwhile the molds are in said one closely spaced position and said tablestructure is in its substantially horizontal position.